1. Technical Field
The present invention relates to an image display apparatus and an image display method, and more particularly, to a technique suitable for an image display apparatus having a display whose characteristic changes depending on temperature.
2. Related Art
In recent years, among image display apparatuses that display various kinds of information as images, an image display apparatus having a non-volatile display is under development for practical use. Since the non-volatile display consumes electric power only at the time of rewriting, the power consumption of the non-volatile display is overwhelmingly small as compared with a normal display. Accordingly, since it is possible to make equipment having an image display apparatus small by reducing the capacity of a battery, the non-volatile display has been drawing attention as a display suitable for equipment, such as an electronic book.
As such non-volatile display, there is a display using cholesteric liquid crystal as a display material. Moreover, in the case of using the cholesteric liquid crystal, high-speed image rewriting can be realized using a DDS (dynamic drive scheme) driving method that is a cholesteric liquid crystal driving method disclosed in U.S. Pat. No. 5,748,277.
However, the viscosity of the display material of the non-volatile display easily changes depending on temperature, even though the display material of the non-volatile display is advantageous in that the power consumption thereof is small. That is, there is a problem in that the display material of the non-volatile display has temperature dependency that a display characteristic thereof easily changes depending on temperature. For this reason, in the case of driving cholesteric liquid crystal using the above-mentioned DDS driving method, the change of display characteristics depending on the temperature is large, as also disclosed in U.S. Pat. No. 5,748,277. Accordingly, it is necessary to control driving parameters, such as a voltage applied to the cholesteric liquid crystal, in the unit of temperature change of 1° C. or less, for example.
For this reason, it is necessary to cope with change of the display characteristic occurring due to the temperature difference in a case that was not a problem in the related art, that is, in a case when the temperature difference is found within a display region of the display regarding the temperature of cholesteric liquid crystal, such as a case when a heat source is disposed close to the display. Particularly in the case of a display using a passive driving method, the number of kinds of driving parameters is normally small as compared with a case of an active driving method. Accordingly, change to an optimal driving parameter corresponding to a place where the temperature difference is found is difficult. As a result, display different from original display is performed in a display region where the temperature is different, which causes a problem in that reproducibility of a displayed image is degraded. Particularly in the case when the temperature difference is so large, for example, there is a problem in that a corresponding part is displayed in a completely white or black color.